In the field of lithographic printing plate making, an aluminum plate obtained by a direct chill (DC) casting process has enjoyed wide use as a material of a substrate. In recent years, it has been proposed to use an aluminum plate obtained by a twin-roll continuous casting and direct hot rolling process that is simpler than DC casting (hereinafter simply referred to as a hot rolled plate). For example, U.S. Pat. No. 5,078,805 which corresponds to JP-A-3-79798 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a process for producing an aluminum substrate for a lithographic printing plate, in which an aluminum plate is obtained by continuous casting and direct hot rolling according to the twin-roll method. Manipulations proposed in making use of the hot rolled aluminum plate include the apparatus disclosed in U.S. Pat. No. 5,462,614 which corresponds to JP-A-6-262308 and the process conditions disclosed in EP 0730979 A2 which corresponds to JP-A-8-238860.
However, when a hot rolled aluminum plate is electrolytically etched as is common in the art, the surface tends to dissolve, resulting in formation of a different surface profile from that of conventional plate materials with the electrolytic etching conditions being equal. As a result, the resulting printing plate tends to have inferior appearance or printing performance. It has therefore been demanded to establish conditions for a continuously cast aluminum material to be electrolytically etched without undergoing surface dissolution.